Optical method and means



Dec. 14, 1943. MacL, SMITH ET AL 2,336,508

OPTICAL METHOD AND MEANS Filed Nov. 16, 1940 4 Sheets-Shet 1 21 "6 D 14J,- 22 I I 1 r so IN VEN TORJ. FRANC/S MACLEAN J M/ TH THONA! AQU/NASK/RBY ATTORNEY:

4 Dec. 14, 1943. Mac] sM T ET AL 2,336,508

OPTICAL METHODAND MEANS Filed Nov. 16, 1940 4 Sheets-Sheet 2 I o5INVENTORJ'.

FRAN C15 MACLEAN J'MITH .j THOMAS AQU/NAS K/RBY ATTORNEX Dec. 14, 1943.F. MaoL. SMITH ET AL OPTICAL METHOD AND MEANS Filed Nov. 16, 1940 4Sheets-Sheet 3 T u Hl s il M 6 6 k w: mm 1 7 n 5 i a n w n m a e m '5 A5 mm m 1 W u r 1 4 a a m /m 3 .\.M.\. q I 8 CI 1 a F e no 9 .h 9 8 8 1.

IN V EN TORS.

FRANCIS MACLEAN SMITH THOMAS AQU/NAS K/RBY ATTORNEY Patented Dec. 14,1943 OPTICAL METHOD AND MEANS Francis MacLean 'Smith and Thomas AquinasKirby, New York, N. Y.

Application November 16, 1940, Serial No. 365,914

18 Claims.

This invention in its broader aspectrelates to methods and means forincreasing the effectiveness of an image, whether directly viewed by anobserver or photographed for later reproduction. While designedprimarily to apply to images which are originally formed in whole or inpart by projection and particularly composite images which are formedeither by the projection of two sets of images or of one set of imagesand the reflection of real objects, this invention in certain of itsaspects may be applied also to ordinary rojection or to the directviewing of real objects. Our invention is particularly applicable tosingle or composite images which are viewed in cabinets, but is not solimited.

A use to which our invention is widely applicable is in connection withillusions of a common type which embody composite images, whether fordirect viewing or as a basis for photography. For almost a centurytransparent mirrors angularly disposed between an audience and realobjects have been used to combine into a single unitary visible resultthose objects directly viewed and images of other real objects reflectedby the mirror. In one such illusion known as Peppers ghosts, forexample, actors representing real persons were positioned between anaudience and an angularly and vertically disposed transparent mirrorwhich reflected images of other actors who simulated ghosts and wereactually placed at one side of the transparent mirror and of the stageor of the area visible to the audience, thus apparently merging the twogroups of actors into a single composite scene. This illusion withVariations is described in the United States patent to J. H. Pepper andJ. J. Walker, Number 221,605, dated November 11, 1879. Countlesspermutations of such arrangements have been proposed. For almost half acentury, such illusions have been produced by similar combinations ofpro- J'ected images and reflections of real objects or of'reflections ofa plurality of projected images. It has beenproposed, for example, toproject a motion picture of action upon the rear of a translucent screenbetween which and an audience is angularly disposed a transparent mirrorwhich reflects real objects disposed as in a diorama, the real imageprojected from the motion picture furnishing a foreground or actioncomponent. and the virtual image reflected from the diorama furnishing abackground or setting component which unite to form a composite imagesimulating depth and giving a stereoscopic eflect.

As a matter of convenience, in this specification we use the termforeground component to designate that portion of a composite imagewhich represents the action or central theme of that which we arepresenting. Ordinarily, such representations are of persons or objectsin motion, and the term includes static objects either as principals oras supplementary to moving objects.

' For convenience in the sub-joined claims, we apment of the backgroundcomponent. Similarly,

a background component mayinclude furniture and other stage settingswhich may appear either forward or back of the images representing theactors. In the large majority of cases, however, these components appearto be spaced from each other thus giving an illusion of depth.

A motion picture film embodying a foreground component for use in suchan illusion is produced by photographing persons or other objects makingup foreground action against a background I which is as completely blackas is possible. If the illusion of depth is to be created andmaintained, it is essential that with the image projected from this filmthere be no suggestion what'- ever of a surface surrounding the imageand forming a backgroundsince the appearance of such a surface or evena. suggestion thereof jointly with a foreground component interfereswith the wanted background component which is produced by reflection aspreviously described. An observer should not be conscious of thepresence of the screen or any part thereof. We have found itcommercially possible to secure a negative motion picture of veryexcellent quality in which what would normally be the backgroundiswholly' clear. In printing from this negative a positive 1 film foruse in a projector, however, we have found it practically although nottheoretically impossible to secure complete opacity in that portion ofthe positive film not occupied by the foreground action even though thecorrespondingportion of the negative film appears to be wholly clear.Unless exposure and development of this positive or one of suchprocesses is carried to an extreme which produces an unsatisfactoryforeground image, the remainder of the film permits the passage of acertain amount of light. This light seeps through the positive film, asit were, even by reflection from silver grain to silver grain, andemerges as diffused light, or light ma pass through very smalltransparent spaces suggesting minute pin heads. Even when printing iscarried out under the best commercial conditions, enough light passesthrough this portion of the film which should be completely opaqueseriously to interfere with the effectiveness of the illusion. Also,repeated projection causes scratches in the emulsion, known in themotion picture business as rain," and other damage which still furtherreduces this opacity.

This foreground component of a composite image must be projected upon a.so-called rearprojection screen. Such a screen, indeed, must be usedpractically speaking for all such projection since light bearing animage must be projected upon the rear surface of a flat translucent bodyand the image viewed from the front urface thereof. Projection of lightthrough such a screen causes marked diffusion which as a practicalmatter is added to the diffused and even direct light which passesthrough what should be the opaque portion of the film carrying theforeground component. The result may even appear as a bluish haze orscrim tending to make visible the surface of the screen and apparentlydisposed between the observer and the apparent position of at least aportion of the background component. This surface visibility carried bythis unwanted light in itself interferes with the quality of thereflected background and tends to obscure and confuse it, but moreimportant is the fact that it reveals to the audienc that the foregroundaction is being projected on a surface thus indicating the presence of abackground associated with the action. Since the illusion of depthdepends upon the projection of the foreground action apparently spacedwell apart from a background, including, in many cases, a prosceniumarch and stage setting, which is produced solely by a wanted backgroundcomponent as by reflection as of a diorama, it will be readilyunderstood that this visibility of what should be the opaque and unseenportion of the foreground surface destroys the illusion for which othershave long striven.

As will be evident to those skilled in the art of making dramaticpresentations, there are times when the stage, or in an illusion such asthe one described above, that which passes for the stage, must becompletely unoccupied. In an illusion such an effect is impossible ifthe screen is visible with no foreground component such as figuresrepresenting actors upon it. For example, it is highly desirable thatthe stage appear to be empty at the beginning and end of a presentationsince otherwise much of the dramatic effectiveness is lost. Use ofmethods and means described and claimed herein, so far as we are aware,for the first time makes it possible to accomplish these new anddesirable results in an illusion of this character.

The above difliculty as caused by unwanted light coming from aforeground component is much increased by interfering light from othersources.

Light from a diorama disposed as above described is in part reflected bya transparent mirror to an observer, as is necessary in order to producethe background component, and in part is transmitted through thismirror. A portion of this transmitted light falls upon and rendersvisible the portion of the scren surrounding the image of the action ofthe foreground component which should be maintained completely invisibleif the illusion of a third dimension is to be maintained, as statedabove. .Also this visibility, which is in the form merely of interferinlight and not of images of the object making up the diorama, conflictswith the wanted and ponent.

A primary object of our invention is to overcome the above difficultiestogether with certain related difliculties, as will later appear, whichin the past have caused the failure of all attempts to producecommercially such types of illusions, so far as we are aware. Aparticular object is to maintain the invisibility of the areasurrounding a projected image of a foreground component of a compositepicture which ha the illusion of depth which is produced by combining aforeground component with a reflection of a background component.

Difficulties in some respects similar to the above apply to projectionwithin a cabinet or to any type of rear projection, even when acomposite image is not desired.

For many years pictures of various types have been presented incabinets, either by projection of stereopticon or motion picture type orfor direct viewing. Conditions of use of such cabinets generally haverequired that they be employed in fully light rooms. As a consequencethe definition of details, light and shade, quality and intensity of thepicture as viewed have been seriously diminished by the effects ofinterfering light, which, as reflected back to an observer, is diffusedto a not inconsiderable extent. Similarly it has long been proposed andin a limited measure practiced to show motion or still pictures uponso-called daylight screens likewise in rooms which are darkened only toa limited extent.

. being even greater with the projection of a composite image than withthat of an ordinary single image. Another object of our invention,therefore, is to overcome the particularly damaging effects of outsideinterfering light in connection with such illusions.

We overcome the above difficulties and carry out the objects of ourinvention by simple method and means.

We absorb a portion of this interfering light, whether coming from aforeground component, from a background component or the objects whichmake it up, from the sight opening of a cabinet, or, in those cases inwhich a cabinet is not used, from the room generally within which ascreen is placed. Since the interfering'light which does maximum damagis diffused, we presingle image as distinct from a composite control ofthis interfering light.

for tomake use of a wave filter which has mini mum transmission of lightof those wave lengths which are diffused to a maximum extent and minimumabsorption of those wave lengths relabe used alone to the end that amuch improved image is secured. .We so apply these steps and means thatthey do not interfere noticeably with the images which are wanted whiledisposing of the interfering light which is not wanted.

All-projection lamps are relatively rich in light of the shorter wavelengths, ordinarily spoken our secondary protective reflecting means andfilof as blue. According to accepted optical law,

light "of such wave lengths is diffused to a much greater relativeextent than is light making up the remainder of the spectrum.Consequently by diminishing the light of thi character we reducediffusion to a relatively greater extent than we reduce the totalquantitative value of the light. It is diffused light which producesmuch of the difficulty which we overcome. W therefore prefer tointerpose .a minus-blue filter in the light of the foreground componentand in the interfering light from other sources so that we cut down theamount of light of the shorter wave lengths, ordinarily spoken of asblue light. This reduction in quantitative light value and indeed thequalitative change in sensory color value are so slight that they arepractically imperceptible to an observer yet they destroy or at worstmuch reduce the diffused light which would render 'visible that areawhich we maintain invisible.

Also in rear-projection of a single image, we have found that the use ofa filter particularly of this character is of value in that it reducesthe diffused light coming from front or rear.

which is objectionable with any rear-projection screen.

Another measure which we employ is equally simple and its resultsequally striking. To reduce to a negligible point other interferinglight, notably that coming from or associated with a backgroundcomponent, we place another protective transparent mirror between theprimary refiecting mirror and the rear-projection screen at such anangle that it will reflect this unwanted light away both from the screenand from a viewing station. Likewise this secondary mirror infrom aprojector rather than reflected from a tercepts interfering light comingfrom the viewing station infront of the screen and reflects a portion ofit away from the real image and from the vicinity of the apparentposition of the virtual image. Hence it is also valuable when a image iproduced.

The acute angle at which this secondary mirror is placed relative to theplane of th rear-projection' screen is such that there is minimuminterference with the strong primary image upon that screen. Theintensity of the interfering light in relation to that of theforegroundim'age (and, indeed, to the amount of damage which it does) isso little that steps and means which virtually destroy it are withoutnoticeable effect upon the foreground image.

Our filter also is of benefit in assisting in the -It causes aquantitative drop in intensity on account of transmission losses. Thisquantitative result is independent of the qualitative effect of theparticular filter employed. It'will of course be unwhich will laterappear.

ter asone sheet of plane glass preferably minus- =blue in filter factorreadfly transparent and set at a slight angle to the plane of thescreen.

Further details of the invention and other objects thereof and its novelfeatures will be understood from the following description and drawingsand particularly pointed'out in the ap claims. It will be understood,however, that the invention may be embodied in forms other than thoseshown and within the scope of th broader claims. The detaileddescriptionwhich follows refers to the accompanying drawings whichillus- I trate preferred embodiments.

In the drawings:

Figure 1 is an isometric view partly broken away and partly in sectionand with certain parts omitted for clarity of an exterior of acabinetillustrating the practice of our invention.

Figure 2 is a sectional view of a cabinet illustrating the combinationof a projected picture and a reflected diorama.

Figure 3 corresponds to Figure 2, the background image, however, beinginitially projected diorama.

I Figure 4 shows an embodiment of the invention similar to that ofFigure 1 but includes the lacing or a stage setting, which for purposesof illustration is substituted for a diorama, in a preferred positionwhich adds much to the effectiveness 0f the presentation. a

Figure 4a corresponds to Figure 4 but shows the use of a projectedbackground component in place of real objects. Figure 5 illustratescertain of the optical principles involved in the practice of ourinvention.

Figure 5a represents a film of a type producing a foreground componentof a composite image. Figure 6 (Sheet 2) illustrates the practice of ourinvention as applied to the production of a negative motion'picture filmfrom a composite image formed according to the practice of ourinvention.

Figure 7 (Sheet 1) is a preferred variant of the form of our inventionshown in Figure 3.

- Figure 8 (Sheet 3) is a diagram showing our invention as applied torear-projection genersentially of a projection chamber I I (Figure 4),va viewing chamber I 3, and a background chamber H. The backgroundchamber may be merely a recess in one side of the viewing chamber. In

fact, the various chambers to which we refer in this specification andin the sub-joined claims may be merelyparts of one chamber. A projectingmachine I5 may be disposed within the projection chamber, or, as shownor indicated in Figures 2, 3 and 5, it may be placed directly back of ascreen I! (Figures 1 and 2), sometimes hereinafter called a centralsurface for reasons This latter arrangement is of course a common onewhen our invention is practiced in a theatre. The projector maygenerally is the latter. If desired, in the structures shown in Figures1, 2 and 3, the projector may be placed in a projection chamberpreferably located below the viewing chamber, and the image reflected bysuitable mirrors upon the screen IT.

The projection chamber l2 and background chamber I4 make up a roughlyquadrilateral box with the background chamber l4 shown in Figure 2 asabove the projection chamber. An observer looks from a viewing stationthrough a protective window l8 as seen in Figure 2 placed in a forwardsight opening l9 or as shown in Figure 6 a camera may be substituted forthe observer. All other sides of the housing are closed, except thatthrough which images are projected. The window 18 has no opticalfunction and is intended merely to keep out of the apparatus the headsand fingers of observers who are curious as to how the illusion isobtained. In those locations in which external reflections aretroublesome it may be omitted.

In the background chamber of Figure 2, a diorama is indicated containingfor example a far background 2| disposed upon a wall of chamber I4, andwings '22 and 23 making up a stage setting, and, if desired, asimulation of a proscenium arch 24. In combination with a minus-bluefilter, we have found blue an excellent color for the diorama or in factany background component. The blue character of the one componentimparted by the filter well cooperates with the slightly amber tone ofthe other component, to use sensory terms, to heighten the effect ofdepth and the effectiveness of the illusion, even though an observer maynot be conscious of any color sensations as such. It is particularly tobe noted, however, that the effectiveness of the methods and meansherein described and claimed is in no way dependent upon this use ofcomplementary colors. although it may be much assisted thereby. Thediorama is illuminated as by an incandescent lamp 25 with a reflector 26set in a housing 21 which if desired may be ventilated. In practice aplurality of light sources is used, but only one is shown for purposesof illustration.

A primary transparent mirror 28 is vertically and anguiarly disposed andcomprises a front surface 29 and a rear surface 30. The angle at whichthe mirror is to be set depend upon the placing of the other elements ofthe device and the results which are desired, but an angle of forty-fivedegrees, as shown in Figure 5, is common. In practice for most purposeswe prefer to employ a plane sheet of plate glass, but for certain usesthe mirror may be silvered lightly.

Transmission relatively to reflection should be 7 high. As will bereadily understood by persons skilled in this art, light from sources 25is reflected from the objects making up the diorama and upon theforwardly facing surface 29 of the transparent mirror 28, whichthereupon forms virtual images which make up a background component.

The optical principles involved will be clear by a consideration ofFigures 1, 2 and 5. As shown in Figure 2, the optical axis of a cone oflight representing a portion only of the diorama is indicated in dot anddash line as ABC and a projection of a portion CB of this line as CBC'Bbecomes the optical axis of the projector l5 which is producing theforeground component. DEF represents the actualreflection toward anobserver 0 of point D of the diorama and GHI that place between thecentral surface I1 and the of an opposite point G. Similarly line JKLrepresents the actual reflection of point J toward the observer. Theobserver, however, views this background component, except that portionthereof which represents the proscenium arch, as if it were projectedbackwardly as indicated by the dotted lines HGG, KJJ and EDDrespectively and disposed to the rear of the screen I! in the planesindicated by the dotted lines extending upwardly from GG, JJ and DDrespectively which of course represent the planes of the respectivevirtual images. The proscenium arch properly appears as if before thescreen II in the double plane indicated by dotted lines PP, whichrepresent its virtua1 image. Therefore screen I! bearing a real imagewhich forms a foreground component later discussed becomes a centralsurface since it appears as if central between the virtual image of theproscenium arch in the plane represented by PP and the remainder of thebackground along the planes represented as proceedingfrom GG, JJ and DD.The various elements making up each component need not be or appear tobe in planes parallel to each other or to those of the other component.For example, the impression of perspective in a background componentrepresenting scenery may be heightened if its plane is slightlyinclined. In the sub-joined claims, we speak of foreground andbackground components as disposed in adjacent planes, or as soappearing. We do not limit ourselves to a composite image in which theseplanes are but little separated, but wish merely to make clear that theplanes must be sufficiently close to each other so that the resultingcomposite image has psychological unity.

A foreground component may be provided by a positive film 32, which ofcourse is printed from a negative. As shown for purposes of illus-'tration in Figure So, this positive film comprises essentially abackground 33 and a figure 35, here.

shown as that of a dancing girl, which when projected create the trueforeground component. As previously explained the area 33 of the film 32surrounding the figure 35 must be completely opaque unless the illusionis to be destroyed. In Figure 5a light leakage or lack of opacity inarea 33 is represented in an exaggerated form.

By means of the projector I5 a relatively intense image representingthis .foreground component is projected upon the central surface ll. Anobserver 0 is able to see this image without realizing the presence ofthe transparent mirror 28. In addition to maintaining a complete absenceof visibility on the central surface surrounding the figure 35, it isalso desirable to maintain a careful balance between the relativelysubdued image of the diorama reflected to form the background componentand the relatively brilliant image which makes up the foregroundcomponent.

To overcome the difficulties caused by the visibility of the areasurrounding the foreground component as viewed by an observer, suchdifiiculties having prevented the wide commercial use of all suchillusions so far as we are aware, we

primary reflecting mirror 28 both a secondary transparent mirrordesignated as 40 in Figure 5, and also a filter 4|. This mirror shouldbe of a high degree of transparency, preferably merely a thin planesheet of plate glass. As a practical matter and as shown in Figure 2, weprefer to combine filter and secondary mirror as a single unit 42, butin order to make the scientific basis .are commonly called blue.

of our invention clearer in Figure we show the two elements asseparated, as they may be in fact.

These two elements cooperate in a plurality of I ways to perfect theprojection of such a composite image as above described.

As previously explained, in an illusion of this character a figure forexample making up a foreground component of a composite image must beprojected with its surroundings completely invisible. In Figure 5asection of a total cone of light emanating from a projector not shownis bounded by the lines NM' and PC", but a section of a portion carryingan image such as 35 is shown as bounded by the lines NM and PO.Therefore, considering only one vertical section normal to thelongitudinal axis of light from the projector, the portions of thescreen between N and N and P and P must be maintained absolutelyinvisible while that between N and P bears the wanted image. Since theimage produced by this light as it passes through a film or slide in theprojector I5 is to be viewed from the opposite side of the screen I1,this screen must be translucent and permit emergence of animage-carrying cone shown in section in Figure 5 as bounded by NQ andPR. Passage of light through such a screen causes diffusion. In order tosecure a relatively brilliant image, the color of this screen must be,

relatively light. Screens for rear projection are ordinarily blue whiteor grayish white in sensory terms. According to an accepted law ofoptics, light of shorter wave lengths is diffused to much greater extentthan light of relatively longer wave lengths. The light making up thesecones, including components which should be invisible as well as thosewhich should be visible, coming as from a projector I5, whether equippedwith an incandescent lamp or an arc, isrelatively richer in light of theshorter wave lengths which Consequently light relatively rich in therange of low wave lengths passing through a light colored screen will bediffused to a relatively large extent as indicated in Figure 5 for onebeam taken as illustrative by the dash and double dot lines 43 muchexaggerated for clarity. Also, the light which penetrates thetheoretically opaque portion 33 of the film 32 is largely diffused. As aconsequence of the two factors above, the side of the screen I! towardthe observer is covered by a scrim ghost or haze which is generally bluein character from the standpoint of sensory perception. A relativelydelicate image reflected from the diorama is in effect combined withthis relatively strong image from the projector. haze (from the sensorystandpoint) psychologically interferes with the relatively weakreflected background and causes great damage by rendering visible thearea surrounding the foreground image as that of the dancer 35 therebydestroying the illusion. Merely a suggestion of a background other thanthat of the background component associated with the foreground figurestends to destroy the illusiom By the interposition of a minus-bluefilter 4| preferably between the screen l1 and the primary mirror 28, wereduce this haze or visible sheen to a point where it no'longer destroysthe effect and thus accomplish an important object of our invention.

In the projection of a single picture (as distinct from a component of acomposite) through a translucent screen, diffused light interferes withthe detail, clarity, and brilliance of the -feres with the enjoyment ofthe picture.

image, although to a less extent than in connection with the creation ofa composite image as described above. Although in the projection ofanordinary single picture, as distinct from a composite picture, anobserver may not be conscious of this haze, it. none the less inter- Arelated object of our invention is to overcome this difliculty.

By using a filter which removes a substantial portion of light of therelatively short wave lengths we effect a qualitative rather than aquantitative change in the light forming our primary image upon thecentral surface. By removing the so-called blue light which is diffusedto a greater extent than any other, we reduce diffusion to an extentrelatively much greater than we reduce total light.

In sensory terms, a minus-blue filter is called amber. An image which isamber in color is supposed to be warm and pleasing. Whateverpsychological benefit flows from this supposedly desirable quality ofthis color we secure but our choice of the filter is based upon soundphysical reasons. Moreover, from the sensory standpoint, the colorchange imposed by the filter is so little as not to be noticed by theordinary observer, but it should be stated that this fact does notnecessarily indicate that the use of a 'a psychologically pleasing colorthough not noticed as a color is not of value.

While We much prefer to use a minus-blue filter, filters of maximumimpenetrability by other sections of the spectrum may be employed.

' Since as already stated the light which we wish to remove is ofrelatively much less brilliance than that making up the foregroundcomponent, it is practicable to absorb a reasonable.

amount of the total light of the foreground component in the process ofeliminating the unwanted interfering light. It is to be noted that weabsorb no light whatever from the relatively weak background component.factor of any filter is of course helpful on a quantitative basis but weprefer but are not compelled to secure the qualitative as well as thequantitative effect of a minus-blue filter.

This filter has other and important uses as will later appear.

The above difliculty caused by projected light,

. largely diffused, is accentuated by light reflected This bluish lineA'STU passes through the two surfaces of the primary mirror 28 and ifunimpeded would reach the screen I! and render it visible. A portion isof course reflected by surface 29. If all of this unwanted light reachedthe central surface II, it would be suflicient to combine with thediffused projected light previously discussed and very seriously toimpair the quality of the composite image. In fact this light alone andwithout the deleterious effects of the difiusedlight may be enough todestroy the effectiveness of the illusion.

A primary method of avoiding this difliculty is by reflecting a majorportion of this light away from the screen I! by the secondary in- Theabsorption that a portion of beam ASTU is reflected by miror 40 as shownby a dash line 8V to the bottom of the viewing chamber, which ispreferably made dead black so that further reflection is prevented. Aportion of this beam which as shown by a dash and dot line ST istransmitted by the transparent mirror 40 is absorbed by the color filterII. In such cases as we actually use the color fllter 4| as separatefrom the transparent mirror ll, further reflection TW takes place backto the mirror 40 andinpartbaclragaintothe fllter ti and so on until theemergent beam is too weak to. be of consequence. Internal reflection ina single element in such cases as we elect to combine fllter 4| andprotective mirror 40 would produce somewhat the same effect. As ourinvention -is shown in Figure 2, however, the decreased transmission onaccount of the filter factor reduces to a" low value the intensity ofthe interfering light which actually reaches the screen II.

A portion of this interfering light, and as will laterbe explained otherinterfering light, does reach the screen II as at U and is reflectedtoward the observer, as for-one theoretical beam only indicated by lineUK. It will of course be understood that this reflected light isrelatively weak. On what might be termed its return trip, however, itencounters fllter 4| and protective mirror II which reduce it to such anegligible point that it is no longer a factor. were able to penetratebeyond the protective mirror 40 and within a fleld of vision it would beagain reflected in part by surface 30 of the primary mirror 28downwardly as shown in Figure 5 and out of the observer's fleld. As amatter of fact, the surface of screen ll toward an observer must berelatively rough and consists of a multitude of small particles.Consequently this (and other) interfering light, considered from thestandpoint of a considerable quantity of it, is reflected, not so muchas shown by ox. but more directly back toward an ob-v server. Also,since the screen must be translucent permit light from the projector topenetrate,

a portion of this interfering light before reflection also penetrates toa certain extent and consequently after reflection is in part diffused.

It of course must be understood that as a matter of fact much of thesingle section of the screen l'l represented by the line NP from time totime is not occupied by an image which the audience should see butrepresents the surroundings of that image which must be kept invisible.That is, each image from the fllm 32 is instantly succeeded by another,a section of which in any given plane is likely to be different from thepreceding section in the same plane. For purposes of convenience, inthis specification and in the appended claims the singular term imagehas been used, but it must be understood to include a succession ofdifferent images succeeding each other.

Not all interfering light, however, comes from the diorama andprojector. projection chamber through the opening IS. A portion is cutall by an apertured member having bailles l8 and 41 (Figures 1 and 2)set above and below the screen I1. If desired, this member may itselfform a proscenium arch or other decorative feature. So-called shadowboxes, not shown, projecting forwardly toward an observer from theviewing opening and other devices may be used further to reduce theinterfering light, but they are clumsy, space-consuming and not Muchenters the In fact 11' it asset cos clined mirror 40. From Figure 5 itwill be seen very effective. Under ordinary conditions disregarding ourparticular arrangement above described, a large portion of thisinterfering light would reach the screen I! and hence would interferewith the effectiveness of an image in general and, an illusion inparticular, An optical axis C'B" of the point A within the diorama imageextended in Figure 5 as B"YZ may be taken as representing a. single pathof interfering light. Stray interfering light will exist within theentire area opposite screen H. The forward surface 29 of the primarymirror 28 reflects a portion B"A' of this interfering light into thediorama where it is helpful rather than harmful. An additional portionfollows B"YZ. The interposition of the secondary mirror 40, however,reflects a portion of this interfering light back upon the rear surface30 of the primary mirror as indicated by the dash and triple dot lineYY'of Figure 5. For reasons stated above in connection with beam A'STU,this light upon reflection is in part diflused. As is clear, a portionof this light is harmlessly transmitted back toward the observer butanother portion YY" is reflected downwardly to the blackened bottom ofthe projection chamber.

Similarly interfering light which may be considered as following the dotand dash line CBC'B', which represents the optical axis of theprojector, is reflected by front surface 29 of the primary mirror as BAinto the diorama where it is helpful. Similarly reflection from thefront surface of protective mirror 40 as indicated by the dash andquadruple dot line CD is reflected to the back surface 30 of primarymirror 28 and as indicated in the quadruple dot line D'E thencedownwardly to the bottom of the cabinet and out of the field of visionof observer 0.

The absorption factor of the filter 4| reduces the intensity ofinterfering light actually reaching the central surface l1, consequentlyincreasing the effectiveness of the image there projected. Itsminus-blue filter factor, if that factor is employed, is particularlyvaluable because much of this interfering light upon its return trip, soto speak, is diffused. It is also to be observed that our use of primaryand secondary mirrors rather than decreasing the eflectiveness of theforeground image increases it by disposing of much of this interferinglight. It will thus be seen that wholly independently of the diorama orof anyother image making up a composite, our system of a plurality oftransparent mirrors angularly disposed between an observer and aprojection l screen increases the efficiency of so-called daylightprojection, as also does our use of a color filter either alone or inconjunction with one or more transparent mirrors.

To illustrate diagrammatically this use of our invention with a singleand protective mirror, in Figure 8 we show a translucent rear projectionscreen 49 in a mount 50 upon which a projector 5| throws an image.Between an observer represented by 0 and the screen a protectivetransparent mirror 52 preferably embodying a filter factor preferablyminus-blue is disposed. The

reflective capacity of this mirror and its position in relation to theimage uponthe screen 49 are such that the observer is not conscious ofany reflection from the screen although the mirror does reflect andabsorb interfering light. So far as we have observed, such a protectivemirror taken alone has no effect whatever in giving to a single imageany impression of depth. Its function is solely protective.

motion or stereopticon, upon a translucent screen 55 protected by atransparent protective mirror 56. This image is reflected by a primarymirror 61 thus creating a virtual image forming a background whichappears in a position indicated by dotted line 58. We prefer to makethis secondary mirror 56 also in the form of a minusblue filter. Aprojector I throws a foreground image upon a translucent screen 6| whichforms a central surface such as I! which in the manner previouslydescribed is protected by a combined transparent mirror and filter 63.

Instead of projecting foreground and background pictures, any desiredcombination of images may be used.

Figure 4 illustrates a preferred variant of our invention in which adiorama or the like may be disposed in a position which increases theeffectiveness of a composite image of which it forms a part.

In a cabinet II having a projection chamber I2 a motion picture or stillprojector I5" may be so disposed that by means of a mirror or prism 65suitably supported as by a bracket 65 an image is projected through atranslucent screen 66 forming a central surface placed at the bottom ofan image chamber 61 equipped with a diagonally disposed primarytransparent mirror 68 and a secondary or protective transparent mirror69 placed between the pimary mirror and screen. If desired, a series ofmirrors may be used. This secondary mirror preferably embodies aminus-blue filter and functions as does the mirror-filter 42 previouslydescribed. To the left of the image chamber as viewed in Figure 4, adiorama chamber 18 may contain a diorama or other small objects or stagesettings. For purposes of illustration a chair 'II is shown.Illumination is furnished as by a battery of lamps of which one 12 isshown. It will be readily understood that the image of the chair II,which of course must be disposed in the diorama upside down in order toappear rightside up in the composite image, will be reflected through anopening "and by the mirror 68. The apparent position of the diorama,that is, its virtual image, is as shown in dotted lines 14 in theprojection chamber I2. If desired, the area I5 surrounding opening 13may be decorated to simulate a proscenium arch a virtual image of whichappears as indicated by dotted lines I5' The image cast by the projectorI5" upon the screen 66 and that reflected from the diorama by I themirror 68 will be seen as a composite by an observer 0 through an'opening I6 of a viewing chamber I3 upon mirror 11 disposed directlyabove transparent mirror 68 and central surface 66.

The positioning of the diorama chamber I8. below the floor of theviewing chamber I3 and with its opening 13 completely shielded from viewor access by an observer is of great value since otherwise the illusionis likely to be diminished or destroyed since an observer is likely topeer within the cabinet and discover the diorama.-

In the arrangement shown in Figure 4 such curiosity cannot be gratified.Also the diorama is completely protected from direct interfering lightwhich might tend in certain circumstances to destroy the desired effect.Obviously the diorama must be illuminated but such illumination may wellbe controlled and standardized as can be done, for example, when thesource or sources 12 represent all of the impinging light. Suchpositioning of a diorama or other objects or simulated stage settings iswithin the object of our invention.

Figure 4a shows an arrangement similar in general construction to thatof Figure 4 but employing a plurality of projectors instead of oneprojector and a diorama or the like.-

Within a projection chamber 8| we dispose a motion picture or stillprojector 82 which by reflection from a mirror or prism 83 projects animage upon a translucent screen 84 forming a central surface. A secondprojector 86, which may be either motion picture or stereopticon, by

' reflection from a mirror or prism 81 and a mirror 88 projects an imageupon a translucent screen 89 which is in line. with a transparent mirror98 which is disposed within an image chamber 9| of which screen 84 formsa portion of the bottom. A secondary or protective transparent mirror92, preferably also embodying a filter, is disposed at an acute angle tothe plane of screen 84 and performs the function previously describedfor mirror-filters 42 and 69. A protective mirror 93 may be used inconnection with screen 88. The virtual image reflected from the realimage projected upon screen 89 is indicated in dotted lines 89'.

.It will be noted that in this instance, as previously stated might bedone, the component which we for convenience term background" actuallyappears as if before the foreground component. The point of this phaseof this construction and method is that two components, one a virtualand the other a real image, are united to form a composite image. Thecomposite image thus formed is reflected by mirror 84 disposed within aviewing chamber 95 and through an opening 96 to an observer 0. It willof course be understood that the operation and principles of this formof our invention are similar to those previously described.

Figure 6 (Sheet 2) illustrates our invention as applied to the making ofa composite photograph. A primary image as for example a foregroundcomponent of a composite picture may be projected as previouslydescribed upon a translucent screen I8I placed in an opening in aviewing chamber I82. Another or second image as previously described maybe formed upon another translucent screen I83 disposed in an opening inanother and contiguous wall of the viewing chamber. Alternatively realobjects may be used. A transparent mirror I84 placed diagonally and inline with these two screens func-- of course be understood that evenwhen both protective mirrors are employed, the photographic intensity ofneither image is seriously reduced but instead the effectiveness of theimages as photograph is increased. If protective mirror I86 is not used,as would be the case when real objects take the place of the pro--jected image, the use of our protective devices and steps does not atall decrease the illumination of the second image, which then can bemade relatively weak if desired.

In the variant of our invention shown in Fig- 6 ure '7 (Sheet 1) we mayemploy two projectors H l and I I2, either motion or still butpreferably motion, in vertical alignment with each other, to form upontranslucent screens H3 and ill a first image and a second imagerespectively, such images being foreground and background componentsrespectively of a composite image. Within a duplex image chamber 6, in arear wall of which screens H3 and Ill are disposed, a totally-reflectingmirror I I1 and a transparent mirror H8 are placed in alignment oneabove I illustrated the secondary or protective transparent mirror andfilter as one integral unit. For.

a majority of purposes we prefer to construct these twoinstrumentalities as one because of simplicity, economy and otherobvious advantages but it is to be understood that they may beconstructed and used separately. In all forms of the invention bothprimary and protective mirrors should be of relatively low reflectingcapacity. For most purposes. sheets of plane glass are adequate. We areaware that'all glass has more or less of color characteristics, but ofcourse in speaking of a filter we refer to a scientifically planned andintelligently employed filter factor, and not to a quality which ishaphazard accidental and unwanted.

It is particularly to be noted that our protective steps and means whenapplied to a composite image neither by absorption or reflection oreither thereof in any manner affect the intensity of a relatively weakvirtual image reflected from real objects making up a backgroundcomponent. Neither do these factors, or either thereof, reduce theintensity of a relatively strong real image making up a foregroundcomponent to a point affecting its visible integrity or photographiceffectiveness. Instead, the application of these measures or either ofthem, appears to increase the brilliance of this compo nent, and, infact of a single image if applied thereto.

The advantages-of our invention will be understood from the foregoingspecification, the

sub --joined claims, and the drawings which form a part hereof. Theyinclude the provision of method and means for creating an improvedcomposite image or an improved single image produced by rear projection,such improvement ,fiowing primarily from the provision of method andmeans for overcoming the harmful effects of interfering light,particularly diffused light, and in positioning the various elements inan improved relation with each other.

We claim: 1. In-an optical device, a chamber with a viewing opening atone side, a primar transparent mirror angularly disposed in relation tosaid viewing opening and in line therewith, means for causing saidprimary transparent mirror to reflect a first or virtual image to apredetermined plane, said first image being one component of a compositeimage, a translucent screen disposed in said chamber in line with saidprimary mirror and with said viewing opening and in a plane adjacent butslightly separated from that of said virtual image, a projector disposedin the rear of said screen for placing a second image upon said screenduring the existence of said first or virtual image formed by saidtransparent mirror, said second image being another component of saidcomposite image, and a second or protective transparent mirror disposedbetween said screen and said primary transparent mirror and invertically angular relation to each thereof, said protective mirrorbeing so disposed in accordance with optical law that the opposite facesthereof reflect interfering and unwanted light out of an observer'sfield of vision without materially reducing the visibility of saidcomposite image.

2. man optical device, a chamber with a viewing opening at one side, aprimary transparent mirror angularly disposed in relation to saidviewing opening. means for causing said primary transparent mirror toreflect a first or virtual image to a predeterminedplane, said imageforming one component of a composite image, a translucent screendisposed in said chamber in a plane adjacent but slightly separated fromthat of said virtual image reflected by said primary mirror, means forplacing a second image upon said screen while said virtual image is inexistence, said second image forming another component of said compositeimage, and a second or protective transparent mirror including aminus-blue filter factor disposed between said screen and said primarytransparent mirror and in vertically angular relation to each thereof,said protective mirror being effective to reduce the amount ofinterfering light affecting said composite image without interferingwith said reflected image.

3. In an optical device, a chamber with a viewing opening at one side, atranslucent screen disposed in said chamber in line with said opening,means for creating an image upon said screen, and a transparent planeminus-blue filter formin a transparent mirror disposed between saidscreen and said opening and in line with each thereof and in acuteangular relation to said screen and adjacent thereto.

4. In an optical device, a chamber with a viewing opening at one side, atranslucent screen disposed in said chamber in line with said opening, aprojector for creating an imag upon said screen, a source of light forsaid projector rich in blue, and a minus-blue plane transparent filterdisposed in line with said viewing opening and said screen and disposedin acute angular relation to said screen and adjacent thereto.

5. In an optical device, a first chamber formed with a viewing openingat one side, a second chamber adjacent said first chamber and having anopening communicating with said first chamber, real objects representinga stage setting or the like being disposed in said second chamber, meansfor illuminating said objects, a primary transparent mirror angularlydisposed in relation to said viewing opening and in line therewith andwith said objects within said second chamber for reflecting from saidobjects to a predetermined plane visible from said opening a virtualimage of said objects when they are illuminated by said illuminatingmeans, said reflected image being on component of a composite image, atranslucent screen disposed in said chamber adjacent but slightlyseparated from the plane of said virtual'image, a projector disposed inthe rear of said screen for projecting an image upon said screen, saidimage being another component of said composite image, and a second orprotective transparent mirror so disposed in accordance with optical lawbetween said screen and said primary transparent mirror in such angularand spatial relation to each thereof that opposite faces thereof reflectto points outside of the field of an observers vision interfering andunwanted light without materially reducing the visibility of saidcomposite image.

6. In an optical device, a first chamber with a viewing opening at oneside, a second chamber adjacent to said first chamber and having anopening communicating with said first chamber, real objects representinga stage setting or the like being disposed in said second chamber, meansfor illuminating said objects,a transparent mirror angularly disposed inrelation to said viewing opening and in line therewith and with saidobjects within said second'chamber for refleeting to a predeterminedplane visible from said viewing opening a virtual image of said objectswhen illuminated by said illuminating means, said reflected image beingone component of a composite image, a screen in said first chamber in aplane adjacent but slightly spaced from that of said virtual image, meanfor forming an image upon said screen during the existence of saidvirtual image, said image so formed being another component of saidcomposite-image, 'said image forming means and said transparent mirrorpassing to the region adjacent said composite image unwanted andinterfering light predominantly of a given group of related wavelengths, and a color filter disposed adjacent said composite image andbetween' said screen and said transparent mirror for absorbing thatselected and unwanted portion of the light of said group of wave lengthswhich would otherwise interfere with said composite image therebypreventing said light so absorbed from interfering with said compositeimage while not-correspondingly reducing the over-all visibility of theimage.

'7. In an optical device for producing a com posite image having depthof which a fore- 'jector for creating a second image upon saidgroundcomponent is produced from a motion of an actor, the area surroundingthe image of the actor in said film being'intended to be opaque but infact and by necessity being permeable by light, and said composite imagealso having a background component which is produced by a virtual orreflected image; a screen, means for projecting an image of an actorfrom such a motion picture film upon said screen, means for reflecting avirtual image of a background to a plane adjacent said screen, and meansfor reducing to a negligible value the quantity of such unwanted lightfrom said area surrounding said actor which is transmitted to anobserver of said screen thereby inhibiting the visibility whichotherwise would be imparted to said screen by unwanted light projectedthrough said surrounding areas of said film thereby preventingthe-destruction of the illusion of reality.

8. In an optical device for-producing a composite image having depth ofwhich a foreground component intended to include only an image of anactor is projected upon th rear of a screen from a motion picture film,the area of the foreground component upon said screen surrounding theactor during the projection of said film being intended to be invisible,and said composite image also having a background component which isproduced by a virtual or reflected image; a screen, means for projectingan image of an actor fromsuch a motion picture film upon said screen,means for reflecting a virtual image of such a background in a planeadjacent to that of said screen, unwanted light from said projectingmeans and said reflecting means making visible said area of saidforeground component surrounding the image of said actor, and meansassociated with said screen for reflecting away from an observer'svision said unwanted light thereby reducing to a negligible value thevisibility which otherwise would be imparted to the portions of saidscreen surrounding the image thereupon of the actor.

9. In an optical device, a primary transparent mirror disposed invertical and angular relation to a viewing station, a first translucentscreen disposed upon the side of said transparent mirror relativelydistant from said viewing station and in line with both thereof, a firstprotectiv mirror disposed between said first screen and said primaryreflecting mirror and in acute angular relation to said first screen andadjacent thereto, a first projector for creating a first image upon therear of said first translucent screen, said first image forming onecomponent of a composite image, a second translucent screen disposed inline with said primary transparent mirror upon the side thereofrelatively distant from that upon which said first screen is disposed, asecond protective transparent mirror disposed between said second screenand said primary reflecting mirror and in acute angular relation withsaid second screen and adjacent thereto, and a second proto form avirtual image in a plan adjacent that of said first image but slightlyspaced therefrom thereby furnishing another component of said compositeimage, said first and second protective mirrors being so disposed inaccordance with optical law that both faces thereof reflect interferingand unwanted light out of the vision of an observer of said compositeimage without materially reducing th visibility of said composite image.

10. .A method of creating a composite image in line with a viewingstation which comprises forming by reflection a virtual image in apredetermined plane, said image being a first component of a compositeimage, projecting a real image in a plane adjacent but slightly spacedfrom said virtual image, said real image forming a second component ofthe composite image, intercepting such projected light which is ofrelatively short wave lengths thereby increasing the effectiveness ofthe composite image by reducing the amount of difiusion, and reflectinginterfering light in a direction away from the composite image and fromthe viewing station thereby further increasing such effectiveness.

11. A method of creating a composite image which comprises reflecting toa first-predetermined plane a virtual image of real objects visible froma viewing station, creating a real image in a second predetermined planeadjacent but spaced from the plane of the reflected or virtual image.said images together forming a composite image visible from the viewingstation, said creation of said composite image causing some "un wantedlight adjacent said composite image, maintaining substantially invisiblethe area of said second plane surrounding said real imag by reflectingin a direction away from the viewing station a substantial portion ofsuch unwanted light thereby increasing the effectiveness of thecomposite image.

12. A method of daylight projection which comprises projecting an imageupon the side of a translucent screen opposite a viewing station by alight relatively rich in the shorter wave lengths thereby causingdiffused light to e ate from the side of the screen relatively adjacentthe viewing station, the screen being subjected to interfering lightpassing to it from the general direction of the viewing station,intercepting a portion of such light of the shorter wave lengths therebydecreasing the relative amount of diffused light emanating from thescreen without propontionately reducing the total illumination upon thescreen, and reflecting away from th viewing station and from the screena portion of the interfering light while maintaining the visibleintegrity of the projected image.

13. A method of creating a composite image having depth which comprisesforming a basis for a foreground component by photographing upon anegative film an actor disposed before a background which on account ofthe limitations of photographic technique when reproduced in a positivefilm will be largely but not completely opaque, reproducing saidnegative film as a positive film in which areas surrounding an image ofthe actor are not wholly opaque, projecting the positive film to form areal image of the foreground component upon an image receiving surfacein a predetermined plane, forming a virtual image of a backgroundcomponent in a plane adjacent but slightiy spaced from that of theforeground component, said components uniting to provide said compositeimage, and reducing to a. negligible value light which passes to anobserver from the areas in the positive film surrounding the image ofthe actor while transmitting said image substantially unimpaired therebypreventing the consequent visibility of areas in the foregroundcomponent surrounding the image of the actor from destroying theillusion of reality.

14. A method of creating a composite image having depth which comprisesforming a foreground component by photographing upon a negative film anactor beforea background which on account of the limitations. ofphotographic technique when reproduced in a positive film will belargely but not wholly opaque, reproducing said both unwanted lightwhich is transmitted alon with the reflection from said objects makingup a background component and light which passes to the observer fromthe areas in the positive film surrounding the image of the actor whiletransmitting said image substantially unimpaired thereby preventingvisibility of such areas surrounding an image of th actor in theforeground component from destroying the illusion of reality.

15. A method of creating a composite image having depth which comprisesforming a foreground component by projecting an image of an actor in apredetermined plane, such projected image being intended to besurrounded by areas which are wholly invisible, reflecting a virtualimage of a background component to a plane adjacent but slightly spacedfrom that of the foreground component, said reflecting step necessarilycausing transmitted light to pass toward the image of the actor and theareas surrounding it making up the foreground component, and reflectingto a point outside of the field of vision of a person viewing thecomposite image asubstantial portion of such transmitted light therebypreventing it from rendering visible such areas in the foregroundcomponent, such visibility if present destroying the illusion ofreality.

16. In an optical device, a chamber with a viewing opening at one side,a translucent screen disposed in said chamber in line with said opening,a projector disposed upon the side of said screen opposite said opening,said projector emitting light which is stronger in one group of relatedwave lengths than in others, and a transparent plane filter having atransmission band complementary to said group forming atransparentmirror disposed between said screen and said opening and inline with each thereof and in acute angular relation to said screen andadjacent thereto.

17. A method of producing a composite image having depth which comprisesreflecting a cirtual image of a background component to a predeterminedplane adjacent but slightly separated from a motion picture screen,while said background component is in existence projecting in motion areal image of a foreground component upon the screen, said foregroundcomponent not occupying all of said screen, said background componentand said foreground com-' ponent uniting to form the composite image,and maintaining substantially invisible those portions of the screen notoccupied by the foreground component.

posite image, and thereafter maintaining .sub-

stantiallyinvisible those portions of the screen not occupied by theforeground component.

FRANCIS MACLEAN SMITH. THOMAS AQUINAS KIRBY.

